Nutrition and exercise are deeply connected, yet totally different, areas of expertise. Scroll through any fitness pro’s Instagram, though, and you’re likely to see some nutrition tips—I mean trainers must know what they’re talking about, right? When it comes to fitness and exercise, sure. But when it comes to nutrition, think twice.

It may seem harmless enough to adopt food protocols from your fave fitness pros. After all, without proper nutrition, your exercise goals and performance can go south, and if you only pay attention to nutrition but fail to exercise, you’re missing out on a key fundamental of overall health. So why wouldn’t you seek advice from the person guiding you through your workouts to help ensure you’re also properly fueling in order to power your performance and meet your fitness goals?

The problem with fitness experts giving nutrition advice

“It would make sense that trainers—whose goal is to help their clients—would also want to help them tackle the nutrition side of things,” says Sarah Amelia Wenig, RD, sports nutritionist and founder of New York Nutrition. Wenig worked as a Pilates instructor for years before becoming a dietician and says when she was solely a trainer, her clients often came to her for advice. “But this is problematic for many reasons,” she says.

The first problem? Many trainers, although they could be personally knowledgable about nutrition and what works for them, are not trained or properly certified to give nutrition advice to clients. In fact, popular trainer certification programs, like the ones at American Council on Exercise (ACE) and the National Academy of Sports Medicine (NASM), only offer a general overview of nutrition and make it clear that it’s not enough to qualify trainers to offer nutrition advice.

“In order to fully help someone with nutrition, an understanding of nutrition science is a must—there’s a reason why rigorous academic coursework and qualifications are required to become a dietitian,” Wenig adds.

Part of the extensive undergraduate training registered dietitians receive includes several semesters of food science, explains Julie Stefanski, RDN, spokesperson for the Academy of Nutrition & Dietetics. “Without an in-depth understanding of how the nutritional makeup of foods differ, some trainers and nutrition coaches choose to steer clients toward a very limited set of trendy foods based on opinion,” she says.

And this doesn’t just go for trainers at gyms or studios, BTW. These rules also apply to social media where countless trainers and self-proclaimed fitness influencers or wellness experts are lending nutrition advice without the solid creds to garner giving it.

So if you’re talking to a fitness trainer or see nutrition advice circulating on social media, how do you know what advice is legit or which guidance you should skip? According to the experts, look for these key red flags.

1. Lack of nutrition credentials

This may seem obvious, but if the person giving advice lacks nutrition credentials beyond a personal training certification or an online course, don’t take it. “First, look for someone who is a registered dietitian nutritionist, RD/RDN, or on their way to becoming an RD, especially those with a master’s degree in nutrition, which will soon be required of anyone wanting to become an RD,” says Wenig. “If someone is not an RD, but has a master’s degree or PhD in the nutrition sciences, this means they have studied nutrition for years—not over the weekend in a crash course, for example—and are qualified to give sound nutrition advice, as well as to call themselves nutritionists,” says Wenig.

It’s important to know that lots of different people call themselves nutritionists in the United States since the term is not very well regulated, explains Wenig. “In many states, qualified nutrition professionals are licensed by the state, and you can check what certifications and training are recognized as meeting educational standards as a nutrition expert,” Stefanski points out.

Bottom line: Do not take nutrition advice from fitness experts or influencers who aren’t also registered dietitians or doctors. But even if they have the proper credentials to offer dietary advice, you still need to do a bit more digging to determine if it’s legit.

2. Affiliating or promoting specific product brands

To be clear—there’s nothing wrong with nutrition experts charging for their time or services. But the lines can become blurry when someone is giving nutrition advice while also selling a specific product line or brand (whether it’s directly through sponsorships and endorsements or indirectly via affiliate links).

“People also have to keep in mind that when someone is promoting products, like a protein powder, they are most likely being paid by this company,” says Wenig. Unless, of course, they say otherwise.

Furthermore, when it comes to supplements and protein powders, remember that these are largely unregulated products in the United States, so it’s best to have a professional like an RD help you evaluate what is worth your investment.

“The diet industry is a billion-dollar business in the U.S., and it’s kept alive by people’s hopes that unsubstantiated products will make a difference in their weight or health,” says Stefanski. “If someone is also making money from a product they are recommending, that is often a conflict of interest,” she adds.

3. Lack of sourcing or research to back up claims

Having the proper credentials is always the telltale sign of whether you can take nutrition advice from an expert. But another good indicator that the accredited person is giving solid advice is if they’re able to present sources to back up their claims. How many times have you seen or heard someone say “science shows x claim” without ever pointing you to a specific source?

“This can look like sharing the title/authors of the article, posting the PMID number, or sharing links to the actual studies,” says Wenig. Bear in mind, though, that you still need to do your homework since research can be flawed, biased, or misinterpreted. How big is the study? Is this nutrition advice that several studies have found to be true? Or does there need to be more research conducted? Was the study performed on people who are similar to you in gender, age, and other factors? All these are indicators of how much you can trust the science and extrapolate it to your life.

4. Extreme statements and lofty promises

If something sounds strange, extreme, or too good to be true—listen to your gut. “There’s rarely a need for someone to give up everything they are eating and follow a set meal plan that’s not individualized,” says Stefanski. “Medical conditions, habits, food preparation abilities, and budgets all impact our long-term success and have to be taken into consideration. Rigid nutrition recommendations never lead to success in the long-term.”

Other things to look for? “Faulty nutrition advice often includes specific ‘super foods,’ a promise of rapid weight loss, strange amounts of foods or food combos, rigid menus or eating windows that don’t compliment real-life,” says Stefanski.

And Wenig adds that “a big red flag is when someone makes a very black-and-white statement or categorizes foods as ‘good’ and ‘bad.’” She says she saw a recent example of this when someone shared a social media post claiming that oat milk causes anxiety and depression in everyone. “It caused people in the group [text] to start panicking because they believed for a moment that this may be true and that they would need to cut out oat milk out of their lives,” Wenig recalls. Fortunately for those sipping on an oat latte at this moment (*raises hand*) she says there’s no need to toss it out. Phew!

At the end of the day

Trust trainers and fitness experts to give you exercise advice. If someone does not have the credential “RD/RDN” or an advanced degree in nutrition alongside their name, think twice before taking their recommendations for how you should be eating, and don’t assume that because something has worked for one person, it will also apply to you.